I've never seen such a list and it would be kind of misleading since almost every company produces several different quality lines. In addition, the year a locomotive was produced is crucial in terms of quality. For example, Life-Like used to produce nothing but train set quality junk. Since they were taken over by Walthers, they are now producing top quality products as the Proto 2000 line. Before Atlas started to produce the Silver and Gold lines, many of their locomotives were average at best. RTR Athearns have finer handrails and some revamped tooling but the internals are really not much different than the BB models. AHM/IHC used to produde some awful stuff but their new Premiere line steam engines rank right up there with some of the best. Mantua used to procuce mediocre steam engines but their new lines are very good.
I'd say the only consistent "Cadillac" lines are Kato, Broadway Limited, Bowser, and Stewart. The only consistent "Yugo" lines are Tyco, Model Power, and early Bachmann. Otherwise, I'd post anything you're thinking about buying and we can give you advice.